Undersink water heaters

[chris French]

It's a fair way, with a rather convoluted pipe run from the HW tank to the kitchen taps (and further still to the utility room) So takes a while to get to the kitchen and then a long pipeful of HW left to cool down

While re-jigging things for a bathroom refit, pondering fitting one of those stored HW , under the sink heaters. probably a 2-3 kw 15l jobbie.

Anyone got experience of these things? would probably plumb it in so that it fed the utility room as well, but we don't use the sink in their that often, and dishwasher and washing machine are cold fil only, so the kitchen sink is the only real draw.

Yup, it's heating more water and with electric, but more convenient, less water and wasted heat from the pipes and less gas used to heat the water. And I could probably reduce the times the boiler is used to heat the tank when the only draw off is the bathrooms/toilet.

[Gib Bogle]

We have this, in our upstairs kitchen (main cylinder is downstairs). It's great having almost instant hot water in the sink.

[Tim Lamb]

In message , chris French writes

Likewise. Plus the original plumber decided to use 22mm for a large part of the run.

Ventilated system or...?

I fitted a cheapo 15l Italian unit supplied by Screwfix. The instructions call for a minimum length of supply pipe to allow the water to expand and the fill should be from the cold supply. We have a water softener so I decided to plumb ours from the hot supply. About ten years old now. No problems although I have not checked the sacrificial anode. There is a pressure relief valve (6 bar?) which I fed to a spare inlet on the sink waste. Probably a mistake as a leak could go unnoticed.

Elsewhere on the farm, a tenant installed the set up described by Harry except no pressure regulator. There were regular problems with the relief valve trickling water to waste.

I have no idea of the thermal efficiency but it saves a lot of ear bashing:-)

regards

[Andrew Gabriel]

Generally two types, 3kW which can run from a 13A FCU and will only take the chill off a dribble of water, and 7-10kW which requires an electric shower type supply and cable. Sometimes, same model is available in these two ratings.

[chris French]

In message , harry writes

Nah, if we want to have a bath, or a shower I don't want to be waiting while the tank heats up. and I'd leave the other taps (bathroom and toilets) on the tank, as they are much shorter runs. I'm only considering this cos of the longer runs to the kitchen.

Yup, this si the sort of thing.

[chris French]

In message , Tim Lamb writes

One of the unvented type

I did read about he need for a long enough bit of supply pipe. But actually I would probably mount it in the utility room, where there is a handy alcove, which should give enough space for the run.

[Tim Lamb]

In message , chris French writes

Very much different ball game for a supply from a pressurised system and well beyond my knowledge. Our mains regularly exceeds 5 bar so a pressure regulator would be essential.

My thinking in using the existing *hot* supply was the benefit of softened water (less crud on the heater element) the low supply pressure and the idea that if more than 15l was drawn off cistern water would by then be warm.

regards

[robgraham]

Thanks Chris - you may have given me a solution to a totally similar problem with the addition of a single storey property so lack of head; I hadn't thought of putting the heater in the utility room - serious lack of lateral thinking there.

Is there any reason why the utility room sink and the kitchen sink can't be on the same outlet pipe?

And secondly what do I make of Andrew Gabriel's comment about the 3kw type only supplying a dribble of water ? I want (strictly I want a reduction in ear bashing!) better pressure and not having the wait for ages for the hot water to come through.

Rob

[Dave Liquorice]

It's a loosely correct statement depending on how you define "dribble".

With a 40C temp rise, 10C (winter mains) to 50C (washing up temp), you need 2.8kW for a 1l per minute flow rate.

[John Williamson]

So, 3 or 4 minutes to get enough "hand hot" water to wash a couple of plates or mugs. Sounds like a dribble to me.

[chris French]

In message , robgraham writes

No, they can feed more than one outlet.

Andrew was responding to Harry mentioning of the instantaneous type - like the over the handbasin things you get for handwashing. I'm talking about a plumbed in small stored water type thing. Like this:

so you get pre heated HW at mains pressure.

There are issues to do with the length of the supply pipe, as that is used to take up the expansion of the water (or you need to use an expansion vessel). You can get an idea by looking at these docs:

[chris French]

In message , Tim Lamb writes

I think that would be the only other requirement.

[Adam Aglionby]

Got a 15l undersink along with pumped electric shower in small flat replaced massive HW tank and mixer shower.

The run needs to be 4m of 22mm off top of my head from first stopcock off mains to allow expansion, can put a coil or another expansion vessel in to get the run in my case it was exactly 4m to where it needed to be.

Relief from pressure valve is arranged via a washing machine drain set. Valve got a little dribbly at 4 years old replaced valve for 15 quid.

Warned sacrificial anode pain to get out, so replaced heater at 5 years old when it began to drip slightly from bottom casing. Enamelled steel vessel, can get stainless at more money.

Plugs in, heats in less than 15 mins to scalding if you need it.

These people have always been helpful ,

[Roger Mills]

I can't get my hear round this! How does a 4 metre length of pipe - full of incompressible water - provide any expansion capacity?

[dennis]

Water might be uncompressible (well almost) but pipes aren't unstretchable.

[Roger Mills]

They ain't *very* stretchable - particularly if made of iron. [As far as I know, the material isn't specified - just the length].

[dennis]

When i fitted one I put a non return valve in and a small expansion tank in.